Optimization of melt treatment for in-house recycling of A1 alloy scrap

Abstract

The production of premium quality castings for structurally safe components for aerospace and automotive applications requires that porosity and inclusions be minimized or eliminated to negate their harmful influence on the mechanical properties. Also in order to achieve a competitive advantage in the automotive industry it has become necessary to use Al alloy scrap to keep the cost-down of the material. A riser and runner part of a cylinder head from the gasoline engine of an automobile was used as the Al alloy scrap. For in-house recycling of Al alloy scrap the variations of the content of alloying elements, microstructures, mechanical properties, and volume of inclusions were examined with respect to the frequency of scrap use and the variations of various inclusions were measured according to different melt treatments. The contents of Mg, Si, Ca, and Sr decreased, but Fe increased with the frequency of scrap use. The tensile strength and yield strength of Al alloy scrap were slightly decreased but not significantly changed, but the fracture toughness and elongation to failure almost halved due to the increase of total volume of inclusions according to the frequency of scrap use. The majority of oxide film and inclusions in Al alloy scrap was removed by a fluxing treatment, but the fluxing treatment followed by a treatment in a Gas Bubbling Filtration (GBF) resulted in a significant increase in the volume of oxide film. The fluxing treatment was the most effective in removing the oxides and inclusions from the Al scrap melt.